The most advanced deep water pipe laying technique now in existence has severe limitations which make the cost of laying pipe excessively high. The maximum criteria of presently known methods include a pipe size of 16 inches in diameter, a maximum water depth of 2,000 feet and a reel radius of 27 feet for carrying the pipe. The maximum weight of a fully loaded reel at this radius is about 2,000 tons. Moreover, for pipes of the above size, the above reel radius causes the pipe wrapped on the reel to have a curvature greatly in excess of its elastic bending limit. This requires reforming apparatus for straightening the pipe as it is unwound from the reel and before it is laid on the bottom of the ocean. Such reforming damages the corrosion coating of the pipe and interrupts the pipe laying process. The coating must be repaired before laying of the pipe can proceed. Further, the reel must be stopped at 1,000 foot intervals to install anodes and cannot under any circumstances handle concrete coated pipe. All of the foregoing limitations and requirements increase the cost of laying a pipeline, and in many cases, the cost is so high that pipe laying plans are abandoned before they can be carried out. This is particularly so when the pipeline is laid under an open sea over several miles. In addition, no other known method of laying large diameter (i.e., 20 inches or greater) pipe for water depths greater than 3000 feet.
Typical disclosures which relate to the laying of pipe from surface vessels include U.S. Pat. Nos. 3,855,835 and 3,924,415, British Pat. No. 2884, and Canadian Pat. No. 667,802. All of these disclosures set forth structures which inherently contain some or all of the above limitations.
For the foregoing reasons, a need has arisen for an improved apparatus and method for laying a pipeline at great water depths and over long distances.